1. Technical Field
The present invention relates in general to an improved architecture for conditioning air flow inside data storage devices and, in particular, to an improved system and apparatus for mass balancing aerodynamic spoilers for disk storage devices.
2. Description of the Related Art
Data access and storage systems generally comprise one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to five disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm). Hard disk drives have several different typical standard sizes or formats, including server, desktop, mobile (2.5 and 1.8 inches) and micro drive.
A typical HDD also uses an actuator assembly to move magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over the disk on an air bearing to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
One of the major hurdles in hard disk drive (HDD) development is track misregistration (TMR). TMR is the term used for measuring data errors while a HDD writes data to and reads data from the disks. One of the major contributors to TMR is flow-induced vibration. Flow-induced vibration is caused by turbulent flow within the HDD. The nature of the flow inside a HDD is characterized by the Reynolds number, which is proportional to a characteristic speed in the drive (such as the speed at the outer diameter of the disk), and a characteristic dimension (such as the disk diameter or, for some purposes, disk spacing). In general, the higher the Reynolds number, the greater the propensity of the flow to be turbulent.
Due to the high rotational speed of the disks and the complex geometries of the HDD components, the flow pattern inside a HDD is inherently unstable and non-uniform in space and time. The combination of flow fluctuations and component vibrations are commonly referred to as “flutter” in the HDD literature. The terms “disk flutter” and “arm flutter” refer to buffeting of the disk and arm, respectively, by the air flow. Unlike true flutter, the effect of the vibrations in HDDs on the flow field is usually negligible. Even small arm and disk vibrations (at sufficiently large frequencies, e.g., 5 kHz and higher), challenge the ability of the HDD servo system to precisely follow a track on the disk.
Since the forcing function of vibrations is directly related to flow fluctuations, it is highly desirable to reduce any fluctuating variation in the flow structures of air between both co-rotating disks and single rotating disks. One technology for reducing flow-induced vibration in high capacity disk drives is the aerodynamic spoiler. Spoilers with windows or otherwise mechanically-weakened structures are often effective as spoilers. However, a disadvantage of putting windows or otherwise weakening spoiler structure is that the spoiler may flutter. This is true flutter in the sense that the aero-elastic system composed of the spoiler and the airflow created by the disks has negative damping (i.e., upon deflection, the spoiler amplifies the flow field) in a linear, small amplitude sense. When negative damping occurs, the spoiler executes limit-cycle oscillations, the amplitude of which is limited by either structural failure or non-linear effects.
Attempts to address these problems include stiffening the structure of aerodynamic spoilers, modifying their aerodynamic shape, and reducing disk speed. However, drawbacks to these solutions often defeat the primary purpose of the spoiler, and cause a reduction in the performance of the drive itself, neither of which is desirable. Thus, a system and apparatus for improving the architecture for conditioning air flow inside data storage devices would be desirable.